Turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
Generally, turbochargers use the exhaust flow from the engine exhaust manifold, which enters the turbine housing at a turbine inlet, to thereby drive a turbine wheel, which is located in the turbine housing. The turbine wheel is affixed to one end of a shaft, wherein the shaft drives a compressor wheel mounted on the other end of the shaft. As such, the turbine wheel provides rotational power to drive the compressor wheel and thereby drive the compressor of the turbocharger. This compressed air is then provided to the engine intake as referenced above.
In designing the turbine stage, selection of the turbine stage components is made relative to a preferred performance point. In a simple uncontrolled fixed-nozzle turbocharger system, an uncontrolled turbocharger is designed so that optimal performance is reached at high engine speeds. However, at other speeds the turbocharger provides suboptimal boost or air volume to the engine.
Controlled turbochargers provide improved performance, in that the turbine optimal operating point is already reached at low or medium engine speeds. Generally in a controlled system, when the flow rate of exhaust gases increases and the turbocharging pressure becomes too high, part of the exhaust gases are discharged into the surrounding atmosphere through a wastegate so as to bypass the turbine.
Typically, the exhaust gas flows through a volute defined within the turbine housing or casing. Further, a wastegate passage is also provided which is separated from the volute by an intermediate wall. To provide for wastegate flow, a wastegate port is provided in the wall which port is controlled by a wastegate valve.
The wastegate valve is selectively openable and closable during operation of the turbocharger. In one such arrangement, the flow of exhaust gas through the wastegate passage is generally parallel to the direction of flow in the volute, at least in the region of the wastegate passage. Typically, the turbine inlet flow and wastegate flow extend circumferentially in the direction of the volute. However, the wastegate port opens perpendicular to or substantially at a right angle to these flow directions and as such the wastegate flow enters the wastegate passage in a sideward or axial direction and then turns immediately through a right angle so as to flow circumferentially through the wastegate passage. Hence, this configuration may commonly be referenced as a 90 degree wastegate although the actual turn angle may vary from a 90 degree angle to some extent, such that the turn angle between the inlet direction and wastegate flow direction may be an obtuse angle above 90 degrees or an acute angle below 90 degrees.
The invention relates to an improved wastegate valve for a turbocharger which provides more efficient flow of the exhaust gas through the wastegate port and the wastegate passage. More particularly as to the wastegate valve, this valve typically includes a disc-like valve body which is pivotally supported on the turbine housing so as to open and close the wastegate port. The valve body is moved by an actuator and can pivot into the wastegate port to a first position which closes the wastegate port, and pivot out of the wastegate port to a second position which opens the wastegate port. Therefore, a controlled portion of exhaust gas may flow through the wastegate passage which in turn flows to a turbine outlet, thereby bypassing the turbine.
When in the open position, the valve body has a valve face which faces toward the wastegate port and is canted at an angle relative to a plane spanning the wastegate port. The valve face preferably is oriented so that the valve face angles toward the wastegate passage which serves to redirect the wastegate flow as it passes through the port and turns into the wastegate passage.
The direction toward the wastegate passage is the primary direction toward which all of the wastegate flow needs to be directed. However, in known valve bodies of a wastegate valve, the exhaust gas may spill over the sides of the valve body in non-optimal flow directions transverse to the wastegate passage direction which therefore creates turbulent fluid flow in this region and requires that this turbulent flow be further redirected by the sides of the wastegate passage in order to direct the exhaust gas into the wastegate passage. This reduces the efficiency of the flow through the wastegate port and can create increased back pressure and efficiency losses.
However, the valve body of the inventive wastegate valve includes flow formations which serve to reduce the flow of exhaust gas in non-optimal directions. These flow formations serve to optimize or maximize the flow of exhaust gas in the optimal or primary flow direction as the exhaust gas flow turns through the turn angle.
In a first embodiment, the flow formation is defined by a dished valve face which is formed by a concave shape provided to the valve face. This concave shape may be a true concave shape wherein the valve face curves inwardly about the entire periphery of the valve face. The concave shape also may be a modified concave shape wherein the valve face slopes from the leading and trailing edges of the valve face to the center thereof while the sides possibly could have less or no concavity. The term concave will also be understood to apply to an inclined flat surface that does not have any curvature from the periphery to the center of the valve face.
In a second embodiment, the valve face may be provided with shallow ribs or strakes which extend parallel to the flow direction and serve to direct flow in the primary direction.
In a third embodiment, the flow formation may be a dam that rises from the valve face along a portion of the face perimeter. The dam could be on the trailing edge or more preferably, on the leading edge of the valve face.
As described in further detail herein, these flow formations serve to optimize flow in the primary direction and reduce non-optimal flow in secondary directions transverse to the primary direction.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.